Fix subscript for flags

[meganesu]

Currently, some flags are set based on a particular bit of a value (e.g., BIT 4, L). That text displays with all normal characters, but it should use subscript to make it clear that a particular bit of that value is being used (e.g., !rb vs. !r<sub>b</sub>).

This affects the following instructions:

• RLC r
• RLC (HL)
• RRC r
• RRC (HL)
• RL r
• RL (HL)
• RR r
• RR (HL)
• BIT b, r
• BIT b, (HL)